1.ID Rules
2.Class Rules
3. Tag Rules
4. General Rules
The common understanding of efficiency comes from "High-Performance Website Construction" published by Steve Souders in 2009 Starting with "Advanced Guide", although the book lists it in more detail, you can also view the complete reference list here, or you can view more details in Google's "Best Practices for Efficient CSS Selectors".
In this article I want to share some simple examples and guidelines that I use to write high-performance CSS. These are inspired by the guide to efficient CSS written by MDN and follow a similar format.
1. Avoid excessive restraint
As a general rule, don't add unnecessary constraints.
// Oops
ul#someid {. .}
.menu#otherid{..}
// OK
#someid {..}
#otherid {..}
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2. The descendant selector is the worst
Not only is the performance low, but the code is also very fragile. The html code and the css code are severely coupled. When the html code structure changes, the CSS must also be modified. , how bad this is, especially in large companies, the people who write HTML and CSS are often not the same people.
// It sucks
html div tr td {..}
3. Avoid chain (intersection) selectors
This is similar to the over-constraint situation. A more sensible approach is to simply create a new CSS class selector.
// Oops
.menu.left. icon {..}
// OK
.menu-left-icon {..}
4. Adhere to the KISS principle
Imagine we have the following DOM:
The following are the corresponding rules...
/ / Bad
#navigator li a {..}
// Good
#navigator {..}
5. Use compound (compact) syntax
Use compound syntax as much as possible.
// Oops
.someclass {
padding-top: 20px;
padding-bottom: 20px;
padding-left: 10px;
padding-right: 10px;
background: #000;
background-image: url (../imgs/carrot.png);
background-position: bottom;
background-repeat: repeat-x;
}
// Okay
.someclass {
padding: 20px 10px 20px 10px;
background: #000 url(../imgs/carrot.png) repeat-x bottom;
}
6. Avoid unnecessary namespaces
// Bad
.someclass table tr.otherclass td.somerule {..}
//Good
.someclass .otherclass td.somerule { ..}
7. Avoid unnecessary repetition
Combine repeated rules as much as possible.
// Oops
.someclass {
color: red;
background: blue;
font-size: 15px;
}
.otherclass {
color: red;
background: blue ;
font-size: 15px;
}
// OK
.someclass, .otherclass {
color: red;
background: blue;
font-size: 15px;
}
8. Streamline the rules as much as possibleBased on the above rules, you can further merge Repeated rules in different categories.
// Oops
.someclass {
color: red;
background: blue;
height: 150px;
width : 150px;
font-size: 16px;
}
.otherclass {
color: red;
background: blue;
height: 150px;
width : 150px;
font-size: 8px;
}
// OK
.someclass, .otherclass {
color: red;
background: blue; height: 150px;
width: 150px;
}
.someclass {
font-size: 16px;
}
.otherclass {
font-size: 8px;
}
9. Avoid unclear naming conventionsIt is best to use names that express semantics. A good CSS class name should describe what it is rather than what it looks like.
10. Avoid !importantsIn fact, you should also be able to use other high-quality selectors.
11. Follow a standard declaration order
While there are some common ways to order CSS properties, below is a popular way that I follow.
.someclass {
/* Positioning */
/* Display & Box Model */
/* Background and typography styles */
/* Transitions */
/* Other */
}
12. Organized code format
The readability of the code is directly proportional to the ease of maintainability. Below is the formatting method I follow.
// Oops
.someclass-a, .someclass-b, .someclass-c, .someclass-d {
...
}
// Okay
.someclass-a,
.someclass-b ,
.someclass-c,
.someclass-d {
...
}
// Good practice
.someclass {
background-image :
linear-gradient(#000, #ccc),
linear-gradient(#ccc, #ddd); 1px 1px #ddd inset;
}
Obviously, these are just a few of the rules that I try to follow in my own CSS in order to be more efficient and maintainable. If you want to read more, I recommend reading MDN’s Guide to Writing Efficient CSS and Google’s Guide to Optimizing Browser Rendering.
